Linear position detection devices take many forms including LVDT's, rectilinear potentiometers, and ultrasonics. Cable extension transducers, however, are easier to install and less alignment sensitive. Cable extension linear position transducers are especially advantageous for longer travel ranges since they are more compact that LVDT's and rectilinear potentiometers.
A cable extension linear position transducer typically requires a drum attached to some type of potentiometer and a power spring to provide retraction torque when the drum is rotated against the spring. A cable is attached to the drum and wrapped around the drum leaving a free or outer end which can be attached to a moving item, the position of which is to be detected. As the item moves, it unreels the cable, thereby rotating the drum around which the cable is wrapped. The drum simultaneously turns a potentiometer shaft to which it is affixed, creating a measurable change in resistance output proportional to the length of cable travel. Meanwhile, the power spring is wound tighter as the drum rotates to release a greater length of cable. This power spring is thus able to provide the retraction torque necessary to reel the cable back in. These components are usually joined together by a variety of parts and fasteners.
A problem with existing cable extension linear position transducers is their complexity. They fail to provide the essential functions with a minimum number of parts. Using an excessive number of components increases the difficulty of assembly, requires the use of fasteners, and leads to a higher cost product.
The present invention addresses the foregoing drawbacks of known cable extension linear position transducers.